Ethylene copolymers reacted with metal oxides

ABSTRACT

Melt-reacted blends of ethylene/carboxylic acid copolymers with metal oxides are improved by first incorporating the metal oxide into an ethylene copolymer of LDPE, HDPE, or LLDPE to form a concentrate or masterbatch, then melt-blending a minor amount of the concentrate into the ethylene/carboxylic acid copolymer thereby obtaining a uniform, homogeneous reaction of the metal oxide with the carboxylic acid groups. These melt-reacted blends provide tough molding resins. Especially preferred are melt-reacted blends of EAA with minor amounts of MgO/LLDPE concentrates.

This is a divisional of application Ser. No. 662,322, filed Oct. 18,1984, now U.S. Pat. No. 4,666,988.

FIELD OF THE INVENTION

This pertains to ethylene copolymers having pendant carboxyl groupswhich are reacted with metal oxides.

BACKGROUND OF THE INVENTION

It is known that ethylene copolymers having pendant carboxylic acidgroups are reactive with metal oxides, metal hydroxides, and metalhydrates to form metal salts of at least some of the carboxylic acidgroups. The carboxylic acid groups are usually those provided by acrylicacid or methacrylic acid, or other such olefin acids, when copolymerizedor interpolymerized with ethylene.

The ethylene/carboxyl-containing copolymers preferred in the presentinvention are commercially available, especially those of the type knownas "interpolymer", but may also be of the type known as "graftcopolymers" and "block copolymers". These expressions are known topractitioners of the art. Interpolymers are made by polymerizing amixture of the monomers; graft copolymers are made by grafting olefinacid groups onto a polyethylene chain; block copolymers are thosewherein long polymer chains comprise chain segments of a polymerizedplurality of ethylene units and segments of a polymerized plurality ofthe carboxyl-containing monomer units.

As used herein the expression "olefin acids" refers toolefinically-unsaturated carboxylic acids which are copolymerizable withethylene, especially acrylic acid, methacrylic acid, crotonic acid, and1-buteneoic acid, most especially acrylic acid and methacrylic acid.

Patents which disclose interpolymerizations of ethylene and unsaturatedcarboxylic acids in a steady state reaction at high temperature and highpressure in a stirred reactor in the presence of a free-radicalinitiator are, e.g., Canadian Patent No. 655,298 (and its U.S.counterpart U.S. Pat. No. 4,351,931); U.S. Pat. No. 3,239,270; U.S. Pat.No. 3,520,861; U.S. Pat. No. 3,658,741; U.S. Pat. No. 3,884,857; U.S.Pat. No. 3,988,509; U.S. Pat. No. 4,248,990; and U.S. Pat. No.4,252,924.

Also included as a part of the present invention are polyethylenes and,preferably, certain ethylene interpolymers of the linear low densityvariety, known by the acronym LLDPE. These LLDPE resins aredistinguishable from the non-linear (branched) low density polyethylene(LDPE) made by homopolymerizing ethylene using free-radical initiators;the LDPE resins contain branched chains of polymerized monomer unitspendant from the main polymer "backbone" and generally have densities inthe range of about 0.910 to about 0.935 gms/cc.

The LLDPE resins are also distinguishable from the linear high densitypolyethylene (HDPE) resins by the fact that these LLDPE resins areprepared by interpolymerizing ethylene with enough of a higheralpha-olefin to yield a linear ethylene copolymer which has a density,generally, in the same range of the LDPE. Linear HDPE generally has adensity in the range of about 0.941 to about 0.965 gms/cc. Both HDPE andLLDPE are linear polymers, prepared using a coordination catalyst, e.g.,the well-known Ziegler catalyst, or modifications thereof such as theNatta catalyst.

As used in this disclosure, the expression "ethylene polymers" refers tothe homopolymers (LDPE and HDPE) and the ethylene/olefn interpolymers(LLDPE).

Some teachings about the differences in LDPE, HDPE, and LLDPE resins arefound, e.g., in U.S. Pat. No. 4,327,009. A method of making variousLLDPE resins is disclosed, e.g., in U.S. Pat. No. 4,076,698.

The addition of metal oxides to molten carboxyl-containing ethylenepolymers, e.g., ethylene/acrylic acid (EAA) or ethylene/methacrylic acid(EMAA) is usually done by carrying the metal compounds, as a hydroxideor hydrate, in an aqueous carrier, employing, in some cases, an acidaqueous carrier to solubilize the metal. This causes bubbling of thewater (as steam) and often has deleterious effects on the product soughtto be made. See, e.g., U.S. Pat. No. 4,440,893 which proposes the use ofan acetylene peroxy compound to alleviate bubble formation.

Directly blending dry anhydrous metal oxides (e.g. MgO, CaO, BaO, ZnO)into molten EAA or EMAA can be performed to avoid the use of aqueouscarriers for the metal oxide, but because of the reactivity of thecarboxylic acid groups with the metal oxides, nonhomogeneous blendingoften occurs.

U.S. Pat. No. 4,420,580 discloses that inorganic metal fillers, e.g.polyvalent metal oxides, are made more compatible with a polyolefinresin, e.g., linear low density ethylene copolymers, by incorporating anethylene/acrylic acid copolymer into a molten mixture of thepolyolefin/metal oxide. In these blends, the polyolefin is present insignificantly greater concentration than is the ethylene/acrylic acidcopolymer.

Patents pertaining to ionomers are, e.g., U.S. Pat. No. 3,249,570; U.S.Pat. No. 3,264,272; U.S. Pat. No. 3,322,734; U.S. Pat. No. 3,379,702;U.S. Pat. No. 3,404,134; U.S. Pat. No. 3,649,578; U.S. Pat. No.3,789,035; U.S. Pat. No. 3,969,434; and U.S. Pat. No. 3,970,626.

It is an object of the present invention to provide a means for blendingmetal oxides into molten ethylene copolymers having pendant carboxylicacid groups which avoids the use of aqueous carriers.

Another object is that of blending dry metal oxides into molten ethylenecopolymers having pendant carboxylic acid groups, whereby excessivereaction of the metal oxide with the said acid groups is substantiallyminimized, thereby permitting a more uniform dispersion of the metaloxide to be made.

Yet another object is that of preparing a curable or cross-linkablecomposite comprising an ethylene copolymer, having pendant carboxylicacid groups, and having substantially uniformly dispersed therein atleast one metal oxide.

These objects are substantially attained by the ways and means disclosedherein.

SUMMARY OF THE INVENTION

A substantially uniform dispersion of metal oxide particles in acarboxyl-containing ethylene copolymer is prepared by making amasterbatch blend of metal oxide in LDPE, HDPE, or LLDPE, then blendinga minor amount of the masterbatch with a major amount of thecarboxyl-containing ethylene copolymer. The preferred ethylene polymeris LLDPE.

DETAILED DESCRIPTIONS

The carboxyl-containing ethylene copolymer is one wherein thecarboxyl-containing moiety comprises about 1% to about 40% by wt. of theethylene copolymer. The carboxyl-containing moiety may be any of theolefin acids having 3 to about 2 carbon atoms, such as, acrylic acid,methacrylic acid, 1-buteneoic acid, crotonic acid, maleic acid, maleicanhydride, and the like, especially acrylic acid and/or methacrylicacid. These copolymers generally have melt flow values (MFV) in therange of about 1 g/10 min. to about 3000 g/10 min. as measured by ASTMD-1238 (Condition E) and, for these type of copolymers, are consideredto be of intermediate to high molecular weight. The preferred range forthe MFV is about 10 g/10 min. to about 500 g/10 min. and the preferredrange for the amount of carboxyl-containing moiety is about 1% to about25% by wt.

The LLDPE resin preferably used is one wherein the alpha-olefincomonomer comprises about 0.2% to about 35% by wt of the interpolymer,the alpha-olefin having from 3 to about 12 carbon atoms, preferably 4 to8 carbon atoms. Preferably the comonomer comprises about 1% to about 20%by wt. of the interpolymer. Octene-1 is an especially preferredcomonomer. A mixture of the comonomers may be used in preparing theethylene interpolymers, such as butene-1/octene-1 or hexene-1/octene-1.These LLDPE interpolymers are generally of intermediate to very highmolecular weight, having MFV's in the range of about 1 g/10 min. toabout 200 g/10 min. as measured by ASTM D-1238(E), preferably about 10g/10 min. to about 70 g/10 min.

The LDPE and HDPE resins which may be used are normally solidhomopolymers having melt indexes (MFV's) in the range of about 1 g/10min. to about 200 g/10 min. as measured by ASTM D-1238(E).

Whereas there are many metal oxides which can be substantially uniformlydispersed in a carboxyl-containing ethylene copolymer by being carriedin LLDPE in accordance with the method of the present invention, it ispreferred that the metal oxide be at least one of the group comprisingCaO, MgO, BaO, and ZnO, all of which are divalent. These divalent metalsare readily available, are inexpensive, and provide beneficialcrosslinking or curing of the carboxyl-containing ethylene copolymerswithout untoward discoloration.

The masterbatch of metal oxide in LLDPE, LDPE or HDPE is convenientlyprepared by mixing at a temperature at which the ethylene polymer ismolten or by any other methods which allow the metal oxide to bedispersed in the polymer, such as dispersing the metal oxide in apolymer solution and then removing the solvent. These ethylene polymershave little or no tendency to react with the metal oxide, thus thereactivity of the metal oxide is preserved for subsequent reaction withthe carboxyl-containing ethylene copolymer. The ratio of metaloxide/ethylene polymer may be virtually any practical ratio whichprovides for efficient loading of the metal oxide into thecarboxyl-containing ethylene copolymer without unduly overloading withethylene polymer. A metal oxide/ethylene polymer ratio in the range of,e.g., 4/1 to 1/20 is particularly operable, though a ratio in the rangeof about 2/1 to about 1/5 is generally preferred; a ratio in the rangeof about 2/1 to about 1/2 is especially preferred.

The mixing of the masterbatch into the carboxyl-containing ethylenecopolymer is done at melt temperatures to provide uniform blending. Theamount of masterbatch per 100 parts of the copolymer is dependent on theamount of crosslinking one wishes to achieve. For example, 6 parts byweight of an ethylene polymer/MgO masterbatch of 1/1 wt. ratio, mixedinto 94 parts by wt. of an ethylene/acrylic acid copolymer (20% A.A. bywt.; MFV of about 300 dg/10 min) crosslinks to a strong tough compositewherein the A.A. groups are about 50%, ±3%, crosslinked. The 3% ethylenepolymer in the composite contributes to the overall strength, toughness,and abrasion-resistance of the final product, as well as serving toimprove the dispersion of the MgO in the EAA copolymer. A convenientblending technique comprises the addition of masterbatch pellets tomolten copolymer; the pellets become substantially uniformly distributedduring the mixing and the distributed pellets disintegrate upon melting.

The preferred LLDPE has a different morphology from the branched-chainLDPE and the linear HDPE. The LLDPE is essentially a linear polymerhaving side-groups (not side-chains) along the polymer backbone due tothe pendent alkyl moiety of the alpha-olefin comonomer which isinterpolymerized with the ethylene. For example, the pendent alkylmoiety of 1-butene is --CH₂ CH₃ and the pendant alkyl moiety of 1-octeneis -(CH₂)₅ CH₃.

The weight ratio of masterbatch/carboxyl-containing ethylene copolymeris variable over a wide range, depending on the amount of metal oxide inthe masterbatch, and is preferably a ratio which will provide a finalcomposition containing about 0.5-100 parts of LLDPE and about 0.5-10parts of metal oxide per 100 parts of the acid copolymer.

Because of the compatibilizing effect of the ethylene polymer in themasterbatch, the metal oxide is more readily and evenly distributed inthe carboxyl-containing ethylene copolymer, thus the reaction betweenthe metal oxide and the carboxyl groups creates a substantiallyhomogeneous final product which is substantially transparent ortransluscent. As a result of this uniform chemical reaction the metalvalues become ionic groups on the copolymer chain and do not function asdiscrete particles or fillers. Fillers are known to form heterogeneous,substantially opaque blends with polymers by way of being inert, withrespect to the polymers, or else by being non-uniformly or irregularlyreacted if there is, in fact, a tendency to react.

The examples which follow are to illustrate particular embodiments, butthe invention is not limited to the embodiments illustrated.

Unless noted otherwise, the polymer properties are measured as follows:

    ______________________________________                                        Physical Property     ASTM Standard                                           ______________________________________                                        Melt Index (M.I.) or Melt                                                                           D-1238                                                  Flow Value (M.F.V.)                                                           Tensile Properties    D-638 and D-1248                                        Tensile Yield         D-638 and D-1248                                        % Elongation          D-638 and D-1248                                        Hardness              D-2240                                                  Tensile Impact        D-1822                                                  Flexural Modulus      D-970                                                   Compression Molding Procedure                                                                       D-1928                                                  ______________________________________                                    

EXAMPLE 1 (COMPARATIVE EXAMPLE; NOT INVENTION)

Fine-particle MgO (3 parts) is blended with 100 parts of anethylene/acrylic acid copolymer (20% A.A., 300 MFV) by beingtumble-blended at ambient temperature for one hour, then the mixture ishand-fed into the hopper of a Werner-Pfleiderer twin-screw extruder. Theextruder (a ZSK-53L extruder) is operated under the followingconditions:

    ______________________________________                                                        Zone Temperatures (°C.)                                ______________________________________                                        Screw (rpm) - 200 Zone       1 - 177                                          Torque (% screw) - 60        2 - 177                                          Throughput (parts/hr) - 60   3 - 163                                          Vacuum at Zone 6 - 30 psig   4 - 163                                          L/D ratio - 45               5 - 163                                          Screw Diameter - 53 mm       6 - 149                                                                       7 - 149                                                                       8 - 149                                          ______________________________________                                    

The extruded resin is found to contain high levels of unreacted MgO,observed as large white specks and was extremely difficult to processdue to the variations in the degree of crosslinking. See Table I belowfor comparison data.

EXAMPLE 2 (EAA PLUS MgO/ETHYLENE POLYMER MASTERBATCH)

Using the ZSK-53L extruder but with extrusion conditions given below,the same EAA polymer of Example 1 is blended with a masterbatch. Themasterbatch is a 50/50 mixture of 700 parts of fine particle MgO and 700parts of an ethylene/1-octene copolymer (25 MFV, 0.921 density, 7%1-octene) prepared in a Banbury mixer with the mixing blades operated atabout 150 rpm for about 5 minutes unto the polymer melts. Once blendedthe masterbatch is cooled and ground into particles. The masterbatch isfed (6 parts/hr.) through a feeder into the twin-screw extruder and theEAA copolymer is fed (50 parts/hr.) simultaneously through a separatefeeder. The extruded resin is clear and contains no visible levels ofunreacted MgO. Because of the increased dispersability the extruder isoperated effectively using a shorter L/D ratio which appreciablyconserves energy.

    ______________________________________                                        ZSK-53L Extruder Conditions                                                                     Zone Temperatures (°C.)                              ______________________________________                                        Screw (rpm) - 200   Zone      1 - 185                                         Torque (% screw) - 50         2 - 255                                         29 psigat Zones 3/4           3 - 255                                         L/D ratio - 24                4 - 285                                         Screw Diameter - 53 mm                                                        See Table I below for comparison                                              data.                                                                         ______________________________________                                    

                  TABLE I                                                         ______________________________________                                        COMPARISON OF BLENDS OF EXAMPLE 1                                             AND EXAMPLE 2                                                                                          Example 2                                                            Example 1                                                                              EAA/MgO--                                                            EAA/MgO* LLDPE                                                ______________________________________                                        I.sub.2 Melt Index (g/10 min)                                                                   2.86**     2.27                                             Tensiles (psi)    3890       4240                                             Yield (psi)       3890       3495                                             Elongation (%)    10         245                                              Izod Impact (-50° C., ft-lb/                                                             0.49       1.82                                             in notch)                                                                     Tensile Impact (ft-lb/in.sup.2)                                                                 33.9       262.4                                            Density (g/cm.sup.3)                                                                            1.168      .964                                             2% Secant Modulus (psi)                                                                         17,000     49,000                                           Flexural Modulus (psi)                                                                          23,000     52,000                                           Visual Appearance hetero-    homo-                                                              geneous    geneous                                          ______________________________________                                         *Severe foaming was observed when the resin was reextruded without vacuum     devolatilization.                                                             **Melt index strand foamed indicating incomplete reaction of MgO with EAA                                                                              

EXAMPLE 3

A masterbatch (concentrate) of MgO/LLDPE, 1/1 ratio, is blended with EAAcopolymer (20% AA, 300 M.I.) using the extruder conditions of Example 2above. The feed rate to the extruder for the EAA copolymer is 75parts/hour while the feed rate of the MgO/LLDPE concentrate is variedfrom 2.51 parts/hour to 3.85 parts/hour thus obtaining different levelsof neutralization of the acid groups. Table II below shows the bulkphysical properties of these blends. In general, as the concentration ofthe MgO in the EAA is increased, an improvement in physical propertiesis observed. This behaviour apparently results from the decreasedmobility of the resin molecules. There also appears to be a limitingpoint where additional amounts of MgO do not cause additional propertyimprovements.

                  TABLE II                                                        ______________________________________                                        BULK PHYSICAL PROPERTY RESULTS                                                FOR VARIOUS EAA/MgO--LLDPE COMPOSITES                                                   % AA Neutralized* (±2%)                                                    35     40      45      52    55                                     ______________________________________                                        I.sub.2 Melt Index                                                                        14.87    8.66    4.53  2.27  .87                                  (g/10 min)                                                                    I.sub.10 Melt Index                                                                       84.14    51.72   29.98 12.95 4.01                                 (g/10 min)                                                                    Melt Tension                                                                              .26      .55     .80   3.8   8.2                                  Tensiles (psi)                                                                            3375     3750    4015  4240  4190                                 Yield (psi) 2645     2750    2745  3495  3595                                 Elongation (%)                                                                            305      315     295   245   150                                  Izon Impact .39      .55     1.22  1.82  .77                                  (-50° C.; ft-lb/                                                       in notch)                                                                     Tensile Impact                                                                            220.3    288.8   300.4 262.5 **                                   (ft-lb/in.sup.2)                                                              Hardness (Shore D)                                                                        65       65      65    65    65                                   Density (g/cm.sup.3)                                                                      .965     .965    .964  .964  .965                                 2% Secant Modulus                                                                         41,000   43,000  44,000                                                                              49,000                                                                              48,000                               (psi)                                                                         Flexural Modulus                                                                          46,000   47,000  47,000                                                                              52,000                                                                              52,000                               (psi)                                                                         Visual Appearance                                                                         clear*** clear   clear clear clear                                ______________________________________                                         *Values obtained from infrared analysis.                                      **Value could not be obtained due to equipment failure.                       ***A clear polymer is an indication of homogeneity.                      

EXAMPLE 4 (COMPARATIVE DATA)

Using the same EAA as in Example 3 above, about 52% of the acid groupsare neutralized with neat MgO and compared with another portion of theEAA which has about 52% of the acid groups neutralized with a 50/50concentrate of MgO/LLDPE. The EAA/MgO blend is prepared in a Banburymixer where the temperature reached about 204° C. The EAA/concentrateblend is prepared in an extruder as in Example 2 above. The physicalproperties in Table III show improved properties using the concentrate;these improvements appear to be caused by the compatibility effect ofthe LLDPE.

                  TABLE III                                                       ______________________________________                                        COMPARISON OF THE PHYSICAL PROPERTIES FOR                                     EAA/MgO COMPOSITE AND EAA/MgO--                                               LLDPE COMPOSITE                                                                           EAA/MgO  EAA/MgO--LLDPE                                                       (52% neut.)*                                                                           (52% neut.)*                                             ______________________________________                                        I.sub.2 Melt Index                                                                          2.71       2.22                                                 (g/10 min)                                                                    I.sub.10 Melt Index                                                                         16.17      12.95                                                (g/10 min)                                                                    Tensiles (psi)                                                                              3505       4240                                                 Yield (psi)   2755       3495                                                 Elongation (%)                                                                              140        245                                                  Izod Impact (-50° C.;                                                                1.67       1.82                                                 ft-lb/in notch)                                                               Tensile Impact                                                                              181.8      262.4                                                (ft-lb/in.sup.2)                                                              Hardness (Shore D)                                                                          70         65                                                   Density (g/cm.sup.3)                                                                        .965       .964                                                 2% Secant Modulus                                                                           41,000     49,000                                               (psi)                                                                         Flexural Modulus                                                                            44,000     52,000                                               (psi)                                                                         Visual Appearance                                                                           cloudy**   clear                                                ______________________________________                                         *Values obtained from infrared analysis.                                      **A cloudy polymer is an indication of heterogeneity.                    

EXAMPLE 5

In similar manner to the foregoing examples and comparisons, it is foundthat LDPE and HDPE, when mixed with MgO as a masterbatch concentrate,also improve the dispersivity of the MgO in the EAA copolymer, but LLDPEis preferred for such concentrates.

EXAMPLE 6

Blends of ethylene/carboxylic acid copolymers with minor amounts ofmetal oxide/ethylene polymers prepared in accordance with the presentinvention provide useful molding compositions and coating compositions.For example, the following melt-reacted blend is found to be useful,when compounded with fillers, colorants and the like, as injectionmolded or compression molded coverings for articles where toughness andscuff-resistance are needed, such as golf balls.

94% of EAA (20% AA, 300 M.I.)

6% of masterbatch of 1/1 ratio of MgO/LLDPE, where MgO is finely dividedand LLDPE contains about 7% 1-octene interpolymerized with ethylene andhas a density of about 0.92 gm/cc and M.I. of 25.

The above ingredients are melt-blended in an extruder where the LLDPEcauses the MgO to be uniformly distributed throughout the EAA and ahomogeneous reacted ionomer is formed.

We claim:
 1. A method for uniformly blending a minor amount of metaloxide into a major amount of molten ethylene/carboxylic acid copolymer,said method comprisingpreparing a masterbatch of metal oxide/ethylenepolymer, wherein said ethylene polymer is selected from the groupcomprising LDPE, HDPE, and LLDPE, adding, with mixing, said masterbatchwith said molten copolymer under conditions at which the metal oxidereacts with the carboxylic acid groups, thereby obtaining asubstantially homogeneous, substantially uniformly reacted product. 2.The method of claim 1 wherein the ethylene polymer is LLDPE.
 3. Themethod of claim 1 wherein the ethylene polymer is LDPE.
 4. The method ofclaim 1 wherein the ethylene polymer is HDPE.
 5. The method of claim 1wherein the ratio of metal oxide/ethylene polymer in the masterbatch isin the range of about 4/1 to about 1/100.
 6. The method of claim 1wherein the ratio of metal oxide/ethylene polymer in the masterbatch isin the range of about 2/1 to about 1/20.
 7. The method of claim 1wherein the ratio of metal oxide/ethylene polymer in the masterbatch isin the range of about 2/1 to about 1/2.
 8. The method of claim 1 whereinthe metal oxide is at least one of the group comprising CaO, MgO, BaO,and ZnO.
 9. The method of claim 1 wherein the metal oxide is MgO. 10.The method of claim 1 wherein the ethylene/carboxylic acid copolymer isethylene/acrylic acid copolymer or ethylene/methacrylic acid copolymer.11. The method of claim 1 wherein the ethylene/carboxylic acid copolymeris ethylene/acrylic acid copolymer.
 12. The method of claim 1 whereinthe ethylene/carboxylic acid copolymer is an ethylene/acrylic acidcopolymer containing about 1% to about 40% by weight of the acrylic acidmoiety, having a melt flow value in the range of about 10 g/10 min. toabout 3000 g/10 min.,and the ethylene polymer is LLDPE having about 0.2%to about 35% by weight of the ethylene moiety, the remainder being ahigher olefin moiety having from 3 to about 12 carbon atoms, having amelt flow value in the range of about 1 g/10 min. to about 200 g/10min., and having a density in the range of about 0.89 to about 0.935g/cc.